Kinetic energy of a hybrid vehicle may be converted into electrical energy via an electric machine in the hybrid vehicle's driveline. In particular, vehicle wheel torque may be converted into electrical energy via the electric machine, which may be referred to as regenerative braking. The electrical energy may be stored in an electrical energy storage device until it is subsequently used to propel the vehicle. The electric machine may have a larger inertia if the electric machine provides a substantial amount of torque to propel the vehicle. The larger inertia may be related to the number windings in the electric machine and the mass of the electric machine's armature. An electric machine having a larger inertia may be utilized to provide a desired rate of vehicle acceleration. However, the electric machine's larger inertia and/or magnetic field strength may make it more difficult to mitigate the possibility of wheel locking during wheel braking if the electric machine is providing regenerative braking. It may be desirable to provide regenerative braking while at the same time providing anti-lock wheel control during vehicle braking so that the vehicle may decelerate at a desired rate and so that at least a portion the vehicle's kinetic energy may be captured.
The inventors herein have recognized the above-mentioned issues and have developed a vehicle operating method, comprising: adjusting a regeneration torque of a primary axle to a lower magnitude value of a low pass filtered primary axle regulation torque of a right wheel and a low pass filtered primary axle regulation torque of a left wheel in response to activation of an anti-lock braking system.
By adjusting a regulation torque of a primary axle in response to a lower magnitude value of a low pass filtered primary axle regulation torque of a right wheel and a low pass filtered primary axle regulation torque of a left wheel in response to activation of an anti-lock braking system, it may be possible to provide regenerative vehicle braking while also regulating vehicle wheel speed even if an electric machine of a driveline has a larger inertia. In one example, regulation torque of a wheel may be decomposed into a regenerative braking torque and a friction braking torque. The regenerative braking torque of a wheel may include lower brake regulation torque frequencies and the friction braking torque of the wheel may include higher regulation torque frequencies so that electric machine torque does not have to respond to the higher wheel regulation torque frequencies. On the other hand, the friction brakes may respond to higher wheel regulation torque frequencies so that the possibility of wheel lock may be reduced while regenerative braking is in progress. Additionally, regenerative braking torques and friction braking torques of a secondary axle may be responsive to other regulation torque frequencies to compensate for inertia of other electric machines providing regenerative braking to the secondary axle and vehicle weight distribution.
The present description may provide several advantages. For example, the approach may improve storage of a vehicle's kinetic energy into electric energy. Further, the approach may reduce the possibility of wheel locking even if the vehicle includes an electric machine with a larger inertia and/or magnetic field. Additionally, the approach compensates wheel torque control during conditions where regenerative braking may be limited because of unusual vehicle operating conditions.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.